U.S. patent application number 11/260806 was filed with the patent office on 2007-06-28 for methods for making holographic data storage articles.
This patent application is currently assigned to General Electric Company. Invention is credited to Eugene Pauling Boden, Christoph Georg Erben, Brian Lee Lawrence, Kathryn Lynn Longley, Xiaolei Shi.
Application Number | 20070146835 11/260806 |
Document ID | / |
Family ID | 37963972 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070146835 |
Kind Code |
A1 |
Erben; Christoph Georg ; et
al. |
June 28, 2007 |
Methods for making holographic data storage articles
Abstract
A method of making a holographic data storage medium is
provided. The method comprises: (a) providing an optically
transparent substrate comprising at least one photochemically
active dye; and (b) irradiating the optically transparent substrate
at at least one wavelength at which the optically transparent
substrate has an absorbance in a range from about 0.1 to 1, to
produce a modified optically transparent substrate comprising at
least one optically readable datum and at least one photo-product
of the photochemically active dye. The at least one wavelength is
in a range from about 300 nanometers to about 800 nanometers. The
optically transparent substrate is at least 100 micrometers thick,
and comprises the photochemically active dye in an amount
corresponding to from about 0.1 to about 10 weight percent based on
a total weight of the optically transparent substrate.
Inventors: |
Erben; Christoph Georg;
(Clifton Park, NY) ; Boden; Eugene Pauling;
(Scotia, NY) ; Longley; Kathryn Lynn; (Saratoga
Springs, NY) ; Lawrence; Brian Lee; (Clifton Park,
NY) ; Shi; Xiaolei; (Niskayuna, NY) |
Correspondence
Address: |
Andrew J. Caruso;General Electric Global Research
One Research Circle
Docket Room K1-4A59
Niskayuna
NY
12309
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
37963972 |
Appl. No.: |
11/260806 |
Filed: |
October 27, 2005 |
Current U.S.
Class: |
359/3 ; 359/4;
G9B/7.01; G9B/7.027; G9B/7.147; G9B/7.148; G9B/7.168;
G9B/7.172 |
Current CPC
Class: |
G11B 7/0045 20130101;
G11B 7/0065 20130101; Y10S 430/146 20130101; G11B 7/246 20130101;
G11B 7/24038 20130101; G11B 7/24044 20130101; G11B 7/245 20130101;
G11B 7/005 20130101; G11B 7/253 20130101 |
Class at
Publication: |
359/003 ;
359/004 |
International
Class: |
G03H 1/02 20060101
G03H001/02 |
Claims
1. A method of making a holographic data storage medium, said
method comprising: (a) providing an optically transparent substrate
comprising at least one photochemically active dye; and (b)
irradiating the optically transparent substrate at at least one
wavelength at which the optically transparent substrate has an
absorbance in a range from about 0.1 to 1, said at least one
wavelength being in a range from about 300 nanometers to about 800
nanometers, to produce a modified optically transparent substrate
comprising at least one optically readable datum and at least one
photo-product of the photochemically active dye, wherein the
optically transparent substrate is at least 100 micrometers thick,
and comprises the photochemically active dye in an amount
corresponding to from about 0.1 to about 10 weight percent based on
a total weight of the optically transparent substrate.
2. The method of claim 1, wherein said at least one optically
readable datum comprises at least one volume element having a
refractive index which is different from a corresponding volume
element of the optically transparent substrate, said volume element
being characterized by a change in refractive index relative to the
refractive index of the corresponding volume element prior to
irradiation.
3. The method of claim 1, wherein the data storage medium has a
data storage capacity, as measured by M/# of greater than 0.5.
4. The method of claim 1, wherein the at least one photo-product is
patterned within the modified optically transparent substrate to
provide the at least one optically readable datum.
5. The method of claim 1, wherein the at least one photochemically
active dye comprises a vicinal diarylethene.
6. The method of claim 1, wherein the at least one photochemically
active dye comprises a nitrone.
7. The method of claim 1, wherein the at least one photochemically
active dye comprises a nitrostilbene.
8. The method of claim 1, wherein the at least one photochemically
active dye comprises a photo-product derived from a vicinal
diarylethene.
9. The method of claim 5, wherein the vicinal diarylethene has the
structure (I) ##STR28## wherein "e" is 0 or 1; R.sup.1 is a bond,
an oxygen atom, a substituted nitrogen atom, a sulfur atom, a
selenium atom, a divalent C.sub.1-C.sub.20 aliphatic radical, a
halogenated divalent C.sub.1-C.sub.20 aliphatic radical, a divalent
C.sub.3-C.sub.20 cycloaliphatic radical, a halogenated divalent
C.sub.1-C.sub.20 cycloaliphatic radical, or a divalent
C.sub.2-C.sub.30 aromatic radical; Ar.sup.1 and Ar.sup.2 are each
independently a C.sub.2-C.sub.40 aromatic radical, or a
C.sub.2-C.sub.40 heteroaromatic radical; and Z.sup.1 and Z.sup.2
are independently a bond, a hydrogen atom, a monovalent
C.sub.1-C.sub.20 aliphatic radical, divalent C.sub.1-C.sub.20
aliphatic radical, a monovalent C.sub.3-C.sub.20 cycloaliphatic
radical, a divalent C.sub.3-C.sub.20 cycloaliphatic radical, a
monovalent C.sub.2-C.sub.30 aromatic radical, or a divalent
C.sub.2-C.sub.30 aromatic radical.
10. The method of claim 6, wherein the nitrone comprises an aryl
nitrone having a structure (IX): ##STR29## wherein Ar.sup.3 is an
aromatic radical, each of R.sup.11, R.sup.12, and R.sup.13 is a
hydrogen atom, an aliphatic radical, a cycloaliphatic radical, or
an aromatic radical; R.sup.14 is an aliphatic radical or an
aromatic radical, and "n" is an integer having a value of from 0 to
4.
11. The method of claim 10, wherein R.sup.14 comprises at least one
electron withdrawing substituent selected from the group consisting
of ##STR30## wherein R.sup.15-R.sup.17 are independently a
C.sub.1-C.sub.10 aliphatic radical, a C.sub.3-C.sub.10
cycloaliphatic radical, or a C.sub.2-C.sub.10 aromatic radical.
12. The method of claim 1, wherein the at least one photochemically
active dye is selected from the group consisting of
4-dimethylamino-2',4'-dinitrostilbene,
4-dimethylamino-4'-cyano-2'-nitrostilbene,
4-hydroxy-2',4'-dinitrostilbene, 4-methoxy-2',4'-dinitrostilbene,
.alpha.-(4-diethylaminophenyl)-N-phenylnitrone;
.alpha.-(4-diethylaminophenyl)-N-(4-chlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(3,4-dichlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-carbethoxyphenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-acetylphenyl)-nitrone,
.alpha.-(4-dimethylaminophenyl)-N-(4-cyanophenyl)-nitrone,
.alpha.-(4-methoxyphenyl)-N-(4-cyanophenyl)nitrone,
.alpha.-(9-julolidinyl)-N-phenylnitrone,
.alpha.-(9julolidinyl)-N-(4-chlorophenyl)nitrone,
.alpha.-(4-Dimethylamino)styryl-N-phenyl Nitrone,
.alpha.-Styryl-N-phenyl nitrone,
.alpha.-[2-(1,1-diphenylethenyl)]-N-phenylnitrone,
.alpha.-[2-(1-phenylpropenyl)]-N-phenylnitrone, and
1,2-bis{2-(4-methoxyphenyl)-5-methylthien-4-yl}-3,3,4,4,5,5-hexafluorocyc-
lopent-1-ene.
13. The method of claim 1, wherein the optically transparent
substrate comprises a thermoplastic polymer, a thermosetting
polymer, or a combination of a thermoplastic polymer and a
thermosetting polymer.
14. The method of claim 13, wherein the thermoplastic polymer is
selected from the group consisting of polyacrylates,
polymethacrylates, polyesters, polyolefins, polycarbonates,
polystyrenes, polyesters, polyamides, polyamideimides,
polyarylates, polyarylsulfones, polyethersulfones, polyphenylene
sulfides, polysulfones, polyimides, polyetherimides,
polyetherketones, polyether etherketones, polyether ketone ketones,
polysiloxanes, polyurethanes, polyethers, polyarylene ethers,
polyether amides, polyether esters, or a combination comprising at
least one of the foregoing thermoplastic polymers.
15. The method of claim 13, wherein the thermosetting polymer is
selected from the group consisting of an epoxy thermosetting
polymer, a phenolic thermosetting polymer, a polysiloxane
thermosetting polymer, a polyester thermosetting polymer, a
polyurethane thermosetting polymer, a polyamide thermosetting
polymer, a polyacrylate thermosetting polymer, a polymethacrylate
thermosetting polymer, or a combination comprising at least one of
the foregoing thermosetting polymers.
16. The method of claim 13, wherein the thermoplastic polymer
comprises a polycarbonate comprising structural units derived from
bisphenol A.
17. The method of claim 1, wherein the at least one photo-product
comprises a photo-decomposition product of the at least one
photochemically active dye.
18. The method of claim 1, wherein the at least one photo-product
comprises a molecular rearrangement product of the at least one
photochemically active dye.
19. An optical writing and reading method, comprising: irradiating
a holographic data storage medium with a signal beam possessing
data and a reference beam simultaneously to partly convert the
photochemically active dye into at least one photo-product and
store the data in the signal beam as a hologram in the holographic
data storage medium; the holographic storage medium comprising an
optically transparent substrate and at least one photochemically
active dye; the optically transparent substrate having a thickness
of at least 100 micrometers, and comprising the photochemically
active dye in an amount corresponding to from about 0.1 to about 10
weight percent based on a total weight of the optically transparent
substrate, and having a UV-visible absorbance in a range from about
0.1 to 1 at at least one wavelength in a range from about 300
nanometers to about 800 nanometers; and irradiating the holographic
storage medium with a read beam and reading the data contained by
diffracted light from the hologram.
20. The method of claim 19, wherein the the read beam has a
wavelength that is shifted by 0 nanometers to about 400 nanometers
from the signal beam's wavelength.
21. A method for using a holographic data storage article, the
method comprising the steps of: irradiating a holographic data
storage medium in the holographic data storage article with
electromagnetic energy having a first wavelength, the holographic
data storage medium comprising an optically transparent substrate
that is at least 100 micrometers thick and comprises at least one
photochemically active dye in an amount corresponding to from about
0.1 to about 10 weight percent based on a total weight of the
optically transparent substrate, said irradiating being done at at
least one wavelength at which the optically transparent substrate
has an absorbance in a range from about 0.1 to 1, and said at least
one wavelength being in a range from about 300 nanometers to about
800 nanometers; forming a modified optically transparent substrate
comprising at least one photo-product of the at least one
photochemically active dye, and at least one optically readable
datum stored as a hologram; and irradiating the holographic data
storage medium in the article with electromagnetic energy having a
second wavelength to read the hologram.
22. The method of claim 21, wherein the second wavelength is
shifted by 0 nanometer to about 400 nanometers from the first
wavelength.
23. The method of claim 21, wherein the first wavelength is not the
same as the second wavelength.
24. The method of claim 21, wherein the first wavelength is the
same as the second wavelength.
25. The method of claim 21, wherein said at least one photo-product
comprises a vicinal diarylethene, a photo-product derived from the
vicinal diarylethene, an oxaziridine, or a decomposition product
derived from the oxaziridine.
26. A method of manufacturing a holographic data storage medium,
the method comprising: forming a film of an optically transparent
substrate comprising at least one optically transparent plastic
material, and at least one photochemically active dye, wherein the
optically transparent substrate is at least 100 micrometers thick;
and comprises the photochemically active dye in an amount
corresponding to from about 0.1 to about 10 weight percent based on
a total weight of the optically transparent substrate, and has a
UV-visible absorbance in a range from about 0.1 to 1 at at least
one wavelength in a range from about 300 nanometers to about 800
nanometers.
27. The method of claim 26, wherein the film of the optically
transparent substrate is formed by a molding technique.
28. The method of claim 26, wherein the film of the optically
transparent substrate is formed by a spin casting technique.
29. The method of claim 26, wherein the at least one optically
transparent plastic material comprises a thermoplastic polymer, a
thermosetting polymer, or a combination of a thermoplastic polymer
and a thermosetting polymer.
30. A holographic data storage medium comprising: an optically
transparent substrate comprising at least one optically transparent
plastic material, at least one photochemically active dye, and at
least one photo-product thereof; said optically transparent
substrate being at least 100 micrometers thick, said
photochemically active dye being present in the optically
transparent substrate in an amount corresponding to from about 0.1
to about 10 weight percent based on a total weight of the optically
transparent substrate, said optically transparent substrate having
a UV-visible absorbance in a range from about 0.1 to 1 at at least
one wavelength in a range from about 300 nanometers to about 800
nanometers; and said at least one photo-product being patterned
within the optically transparent substrate to provide at least one
optically readable datum comprised within the holographic storage
medium.
31. The holographic data storage medium of claim 30, wherein the at
least one photo-product results from a photochemical conversion of
the at least one photochemically active dye during the storage of
data as a hologram.
Description
BACKGROUND
[0001] The present disclosure relates to methods for making and
using holographic data storage articles. Further, the disclosure
relates to holographic data storage articles.
[0002] Holographic storage is the storage of data in the form of
holograms, which are images of three dimensional interference
patterns created by the intersection of two beams of light, in a
photosensitive medium. The superposition of a signal beam, which
contains digitally encoded data, and a reference beam forms an
interference pattern within the volume of the medium resulting in a
chemical reaction that changes or modulates the refractive index of
the medium. This modulation serves to record as the hologram both
the intensity and phase information from the signal. The hologram
can later be retrieved by exposing the storage medium to the
reference beam alone, which interacts with the stored holographic
data to generate a reconstructed signal beam proportional to the
initial signal beam used to store the holographic image. Thus, in
holographic data storage, data is stored throughout the volume of
the medium via three dimensional interference patterns.
[0003] Each hologram may contain anywhere from one to
1.times.10.sup.6 or more bits of data. One distinct advantage of
holographic storage over surface-based storage formats, including
CDs or DVDs, is that a large number of holograms may be stored in
an overlapping manner in the same volume of the photosensitive
medium using a multiplexing technique, such as by varying the
signal and/or reference beam angle, wavelength, or medium position.
However, a major impediment towards the realization of holographic
storage as a viable technique has been the development of a
reliable and economically feasible storage medium.
[0004] Early holographic storage media employed inorganic
photo-refractive crystals, such as doped or un-doped lithium
niobate (LiNbO.sub.3), in which incident light creates refractive
index changes. These index changes are due to the photo-induced
creation and subsequent trapping of electrons leading to an induced
internal electric field that ultimately modifies the refractive
index through a linear electro-optic effect. However, LiNbO.sub.3
is expensive, exhibits relatively poor efficiency, fades over time,
and requires thick crystals to observe any significant index
changes.
[0005] More recent work has led to the development of polymers that
can sustain larger refractive index changes owing to optically
induced polymerization processes. These materials, which are
referred to as photopolymers, have significantly improved optical
sensitivity and efficiency relative to LiNbO.sub.3 and its
variants. In prior art processes, "single-chemistry" systems have
been employed, wherein the media comprise a homogeneous mixture of
at least one photo-active polymerizable liquid monomer or oligomer,
an initiator, an inert polymeric filler, and optionally a
sensitizer. Since it initially has a large fraction of the mixture
in monomeric or oligomeric form, the medium may have a gel-like
consistency that necessitates an ultraviolet (UV) curing step to
provide form and stability. Unfortunately, the UV curing step may
consume a large portion of the photo-active monomer or oligomer,
leaving significantly less photo-active monomer or oligomer
available for data storage. Furthermore, even under highly
controlled curing conditions, the UV curing step may often result
in variable degrees of polymerization and, consequently, poor
uniformity among media samples.
[0006] Dye-doped data storage materials based on polymeric
materials have been developed. The sensitivity of a dye-doped data
storage material is dependent upon the concentration of the dye,
the dye's absorption cross-section at the recording wavelength, the
quantum efficiency of the photochemical transition, and the index
change of the dye molecule for a unit dye density. However, as the
product of dye concentration and the absorption cross-section
increases, the storage medium (for example, an optical data storage
disc) becomes opaque, which complicates both recording and
readout.
[0007] Therefore, there is a need for holographic data storage
methods whereby high volumetric data storage capacities can be
achieved using photochemically active dyes that are efficient and
sensitive to electromagnetic energy, such as light without
interference from the main absorption peak of the dye.
SUMMARY
[0008] Disclosed herein are methods for producing and using
holographic data storage media, which are valuable for reliably
storing large amount of data.
[0009] In one aspect, the present invention is a method of making a
holographic data storage medium. The method comprises: (a)
providing an optically transparent substrate comprising at least
one photochemically active dye; and (b) irradiating the optically
transparent substrate at at least one wavelength at which the
optically transparent substrate has an absorbance in a range from
about 0.1 to 1, to produce a modified optically transparent
substrate comprising at least one optically readable datum and at
least one photo-product of the photochemically active dye. The at
least one wavelength is in a range from about 300 nanometers to
about 800 nanometers. The optically transparent substrate is at
least 100 micrometers thick, and comprises the photochemically
active dye in an amount corresponding to from about 0.1 to about 10
weight percent based on a total weight of the optically transparent
substrate.
[0010] In another aspect of the present invention, an optical
writing and reading method is provided. The method comprises
irradiating a holographic data storage medium with a signal beam
possessing data (or at least one datum) and a reference beam
simultaneously to partly convert the photochemically active dye
into at least one photo-product and store the data in the signal
beam as a hologram in the holographic data storage medium. The
holographic storage medium comprises an optically transparent
substrate and at least one photochemically active dye. The
optically transparent substrate has a thickness of at least 100
micrometers, and comprises the photochemically active dye in an
amount corresponding to from about 0.1 to about 10 weight percent
based on a total weight of the optically transparent substrate, and
a UV-visible absorbance in a range from about 0.1 to 1 at at least
one wavelength in a range from about 300 nanometers to about 800
nanometers. Then the holographic storage medium is irradiated with
a read beam and the data contained by diffracted light from the
hologram is read. In an embodiment, conversion of the
photochemically active dye to at least one photo-product occurs
such that the data storage medium comprises the dye as well as the
photo-product to provide the refractive index contrast needed to
produce the hologram.
[0011] In yet another aspect, the present invention is a method for
using a holographic data storage article. The method comprises
irradiating a holographic data storage medium in the holographic
data storage article with electromagnetic energy having a first
wavelength. The holographic data storage medium comprises an
optically transparent substrate that is at least 100 micrometers
thick, and comprises at least one photochemically active dye in an
amount corresponding to from about 0.1 to about 10 weight percent
based on a total weight of the optically transparent substrate. The
irradiation is done at at least one wavelength in a range from
about 300 nanometers to about 800 nanometers at which the optically
transparent substrate has a UV-visible absorbance in a range from
about 0.1 to 1. A modified optically transparent substrate
comprising at least one photo-product of the at least one
photochemically active dye, and at least one optically readable
datum stored as a hologram is formed. Then the modified optically
transparent substrate is irradiated with electromagnetic energy
having a second wavelength to read the hologram.
[0012] In still yet another aspect, the present invention is a
method for manufacturing a holographic data storage medium. The
method comprises forming a film of an optically transparent
substrate comprising at least one optically transparent plastic
material and at least one photochemically active dye having a
UV-visible absorbance in a range between about 0.1 and about 1 at a
wavelength in a range between about 300 nanometers and about 800
nanometers, said film having a thickness of at least 100
micrometers; wherein the optically transparent substrate comprises
from about 0.1 to about 10 weight percent of the optically
transparent substrate.
[0013] In another aspect, the present invention is a holographic
data storage medium. The holographic data storage medium comprises
an optically transparent substrate comprising at least one
optically transparent plastic material, at least one
photochemically active dye, and at least one photo-product thereof.
The at least one photo-product is patterned within the optically
transparent substrate to provide at least one optically readable
datum comprised within the holographic storage medium. The
optically transparent substrate is at least 100 micrometers thick
and comprises the photochemically active dye in an amount
corresponding to from about 0.1 to about 10 weight percent based on
a total weight of the optically transparent substrate. The
optically transparent substrate has a UV-visible absorbance in a
range from about 0.1 to 1 at at least one wavelength in a range
from about 300 nanometers to about 800 nanometers.
[0014] These and other features, aspects, and advantages of the
present invention may be more understood more readily by reference
to the following detailed description.
DETAILED DESCRIPTION
[0015] Some aspects of the present invention and general scientific
principles used herein can be more clearly understood by referring
to U.S. Patent Application 2005/0136333 (Ser. No. 10,742,461),
which was published on Jun. 23, 2005; and co-pending application
having Ser. No. 10/954,779, filed on Sep. 30, 2004; both which are
incorporated herein in their entirety.
[0016] As defined herein, the term M/# denotes the capacity of a
data storage medium, and can be measured as a function of the total
number of multiplexed holograms that can be recorded at a volume
element of the data storage medium at a given diffraction
efficiency. M/# depends upon various parameters, such as the change
in refractive index (.DELTA.n), the thickness of the medium, and
the dye concentration. These terms are described further in this
disclosure. The M# is defined as shown in equation (1): M / # = i =
1 N .times. .eta. i Equation .times. .times. ( 1 ) ##EQU1## where
.eta..sub.i is diffraction efficiency of the i.sup.th hologram, and
N is the number of recorded holograms. The experimental setup for
M/# measurement for a test sample at a chosen wavelength, for
example, at 532 nanometers or 405 nanometers involves positioning
the testing sample on a rotary stage that is controlled by a
computer. The rotary stage has a high angular resolution, for
example, about 0.0001 degree. An M/# measurement involves two
steps: recording and readout. At recording, multiple planewave
holograms are recorded at the same location on the same sample. A
plane wave hologram is a recorded interference pattern produced by
a signal beam and a reference beam. The signal and reference beams
are coherent to each other. They are both planewaves that have the
same power and beam size, incident at the same location on the
sample, and polarized in the same direction. Multiple planewave
holograms are recorded by rotating the sample. Angular spacing
between two adjacent holograms is about 0.2 degree. This spacing is
chosen so that their impact to the previously recorded holograms,
when multiplexing additional holograms, is minimal and at the same
time, the usage of the total capacity of the media is efficient.
Recording time for each hologram is generally the same in M/#
measurements. At readout, the signal beam is blocked. The
diffracted signal is measured using the reference beam and an
amplified photo-detector. Diffracted power is measured by rotating
the sample across the recording angle range with a step size of
about 0.004 degree. The power of the reference beam used for
readout is typically about 2-3 orders of magnitude smaller than
that used at recording. This is to minimize hologram erasure during
readout while maintaining a measurable diffracted signal. From the
diffracted signal, the multiplexed holograms can be identified from
the diffraction peaks at the hologram recording angles. The
diffraction efficiency of the i.sup.th hologram, .eta..sub.i, is
then calculated by using equation (2): .eta. i = P i , diffracted P
reference Equation .times. .times. ( 2 ) ##EQU2## where P.sub.i,
diffracted is the diffracted power of the i.sup.th hologram. M/# is
then calculated using the diffraction efficiencies of the holograms
and equation (1). Thus, a holographic plane wave characterization
system may be used to test the characteristics of the data storage
material, especially multiplexed holograms. Further, the
characteristics of the data storage material can also be determined
by measuring the diffraction efficiency.
[0017] As defined herein, the term "volume element" means a three
dimensional portion of the total volume of an optically transparent
substrate or a modified optically transparent substrate.
[0018] As defined herein, the term "optically readable datum" can
be understood as being made up of one or more volume elements of a
first or a modified optically transparent substrate containing a
"hologram" of the data to be stored. The refractive index within an
individual volume element may be constant throughout the volume
element, as in the case of a volume element that has not been
exposed to electromagnetic radiation, or in the case of a volume
element in which the photochemically active dye has been reacted to
the same degree throughout the volume element. It is believed that
most volume elements that have been exposed to electromagnetic
radiation during the holographic data writing process will contain
a complex holographic pattern and as such the refractive index
within the volume element will vary across the volume element. In
instances in which the refractive index within the volume element
varies across the volume element, it is convenient to regard the
volume element as having an "average refractive index" which may be
compared to the refractive index of the corresponding volume
element prior to irradiation. Thus, in one embodiment an optically
readable datum comprises at least one volume element having a
refractive index that is different from a (the) corresponding
volume element of the optically transparent substrate prior to
irradiation. Data storage is achieved by locally changing the
refractive index of the data storage medium in a graded fashion
(continuous sinusoidal variations), rather than discrete steps, and
then using the induced changes as diffractive optical elements.
[0019] The capacity to store data as holograms (M/#) is also
directly proportional to the ratio of the change in refractive
index per unit dye density (.DELTA.n/N0) at the wavelength used for
reading the data to the absorption cross section (.sigma.) at a
given wavelength used for writing the data as a hologram. The
refractive index change per unit dye density is given by the ratio
of the difference in refractive index of the volume element before
irradiation minus the refractive index of the same volume element
after irradiation to the density of the dye molecules. The
refractive index change per unit dye density has a unit of
(centimeter).sup.3. Thus in an embodiment, the optically readable
datum comprises at least one volume element wherein the ratio of
the change in the refractive index per unit dye density of the at
least one volume element to an absorption cross section of the at
least one photochemically active dye is at least about 10.sup.-5
expressed in units of centimeter.
[0020] Sensitivity (S) is a measure of the diffraction efficiency
of a hologram recorded using a certain amount of light fluence (F).
The light fluence (F) is given by the product of light intensity
(I) and recording time (t). Mathematically, sensitivity is given by
equation (3), S = .eta. I t L .times. ( cm / J ) Equation .times.
.times. ( 3 ) ##EQU3## wherein I is the intensity of the recording
beam, "t" is the recording time, L is the thickness of the
recording (or data storage) medium (example, disc), and .eta. is
the diffraction efficiency. Diffraction efficiency is given by
equation (4), .eta. = sin 2 .function. ( .pi. .DELTA. .times.
.times. n L .lamda. cos .function. ( .theta. ) ) Equation .times.
.times. ( 4 ) ##EQU4## wherein .lamda. is the wavelength of light
in the recording medium, .theta. is the recording angle in the
media, and .DELTA.n is the refractive index contrast of the
grating, which is produced by the recording process, wherein the
dye molecule undergoes a photochemical conversion.
[0021] The absorption cross section is a measurement of an atom or
molecule's ability to absorb light at a specified wavelength, and
is measured in square cm/molecule. It is generally denoted by
.sigma.(.lamda.) and is governed by the Beer-Lambert Law for
optically thin samples as shown in Equation (5), .sigma. .function.
( .lamda. ) = ln .function. ( 10 ) Absorbance .function. ( .lamda.
) N o L .times. ( cm 2 ) Equation .times. .times. ( 5 ) ##EQU5##
wherein N.sub.0 is the concentration in molecules per cubic
centimeter, and L is the sample thickness in centimeters.
[0022] Quantum efficiency (QE) is a measure of the probability of a
photochemical transition for each absorbed photon of a given
wavelength. Thus, it gives a measure of the efficiency with which
incident light is used to achieve a given photochemical conversion,
also called as a bleaching process. QE is given by equation (6), QE
= hc / .lamda. .sigma. F 0 Equation .times. .times. ( 6 ) ##EQU6##
wherein "h" is the Planck's constant, "c" is the velocity of light,
.sigma.(.lamda.) is the absorption cross section at the wavelength
.lamda., and F.sub.0 is the bleaching fluence. The parameter
F.sub.0 is given by the product of light intensity (I) and a time
constant (.tau.) that characterizes the bleaching process.
[0023] The term "optically transparent" as applied to an optically
transparent substrate or an optically transparent plastic material
means that they have an absorbance of less than 1, that is at least
10 percent of incident light is transmitted through the material at
at least one wavelength in a range between about 300 and about 800
nanometers.
[0024] As defined herein, the term "an optically transparent
substrate" denotes a combination of an optically transparent
plastic material and at least one photochemically active dye, which
has an absorbance of less than 1, that is, at least 10 percent of
incident light is transmitted through the material at at least one
wavelength in a range between about 300 and about 800
nanometers.
[0025] As defined herein, the term "optically transparent plastic
material" means a plastic material which has an absorbance of less
than 1, that is, at least 10 percent of incident light is
transmitted through the material) at at least one wavelength in a
range between about 300 and about 800 nanometers.
[0026] As used herein the term "aliphatic radical" refers to an
organic radical having a valence of at least one consisting of a
linear or branched array of atoms which is not cyclic. Aliphatic
radicals are defined to comprise at least one carbon atom. The
array of atoms comprising the aliphatic radical may include
heteroatoms such as nitrogen, sulfur, silicon, selenium and oxygen
or may be composed exclusively of carbon and hydrogen. For
convenience, the term "aliphatic radical" is defined herein to
encompass, as part of the "linear or branched array of atoms which
is not cyclic" a wide range of functional groups such as alkyl
groups, alkenyl groups, alkynyl groups, haloalkyl groups,
conjugated dienyl groups, alcohol groups, ether groups, aldehyde
groups, ketone groups, carboxylic acid groups, acyl groups (for
example carboxylic acid derivatives such as esters and amides),
amine groups, nitro groups, and the like. For example, the
4-methylpent-1-yl radical is a C.sub.6 aliphatic radical comprising
a methyl group, the methyl group being a functional group which is
an alkyl group. Similarly, the 4-nitrobut-1-yl group is a C.sub.4
aliphatic radical comprising a nitro group, the nitro group being a
functional group. An aliphatic radical may be a haloalkyl group
which comprises one or more halogen atoms which may be the same or
different. Halogen atoms include, for example; fluorine, chlorine,
bromine, and iodine. Aliphatic radicals comprising one or more
halogen atoms include the alkyl halides trifluoromethyl,
bromodifluoromethyl, chlorodifluoromethyl,
hexafluoroisopropylidene, chloromethyl, difluorovinylidene,
trichloromethyl, bromodichloromethyl, bromoethyl,
2-bromotrimethylene (e.g., --CH.sub.2CHBrCH.sub.2--), and the like.
Further examples of aliphatic radicals include allyl, aminocarbonyl
(i.e., --CONH.sub.2), carbonyl, 2,2-dicyanoisopropylidene (i.e.,
--CH.sub.2C(CN).sub.2CH.sub.2--), methyl (i.e., --CH.sub.3),
methylene (i.e., --CH.sub.2--), ethyl, ethylene, formyl (i.e.,
--CHO), hexyl, hexamethylene, hydroxymethyl (i.e., --CH.sub.2OH),
mercaptomethyl (i.e., --CH.sub.2SH), methylthio (i.e.,
--SCH.sub.3), methylthiomethyl (i.e., --CH.sub.2SCH.sub.3),
methoxy, methoxycarbonyl (i.e., CH.sub.3OCO--), nitromethyl (i.e.,
--CH.sub.2NO.sub.2), thiocarbonyl, trimethylsilyl (i.e.,
(CH.sub.3).sub.3Si--), t-butyldimethylsilyl,
3-trimethyoxysilypropyl (i.e.,
(CH.sub.3O).sub.3SiCH.sub.2CH.sub.2CH.sub.2--), vinyl, vinylidene,
and the like. By way of further example, a C.sub.1-C.sub.10
aliphatic radical contains at least one but no more than 10 carbon
atoms. A methyl group (i.e., CH.sub.3--) is an example of a C.sub.1
aliphatic radical. A decyl group (i.e., CH.sub.3(CH2).sub.9--) is
an example of a C.sub.10 aliphatic radical.
[0027] As used herein, the term "aromatic radical" refers to an
array of atoms having a valence of at least one comprising at least
one aromatic group. The array of atoms having a valence of at least
one comprising at least one aromatic group may include heteroatoms
such as nitrogen, sulfur, selenium, silicon and oxygen, or may be
composed exclusively of carbon and hydrogen. As used herein, the
term "aromatic radical" includes but is not limited to phenyl,
pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl
radicals. As noted, the aromatic radical contains at least one
aromatic group. The aromatic group is invariably a cyclic structure
having 4n+2 "delocalized" electrons where "n" is an integer equal
to 1 or greater, as illustrated by phenyl groups (n=1), thienyl
groups (n=1), furanyl groups (n=1), naphthyl groups (n=2), azulenyl
groups (n=2), anthraceneyl groups (n=3) and the like. The aromatic
radical may also include nonaromatic components. For example, a
benzyl group is an aromatic radical that comprises a phenyl ring
(the aromatic group) and a methylene group (the nonaromatic
component). Similarly a tetrahydronaphthyl radical is an aromatic
radical comprising an aromatic group (C.sub.6H.sub.3) fused to a
nonaromatic component --(CH.sub.2).sub.4--. For convenience, the
term "aromatic radical" is defined herein to encompass a wide range
of functional groups such as alkyl groups, alkenyl groups, alkynyl
groups, haloalkyl groups, haloaromatic groups, conjugated dienyl
groups, alcohol groups, ether groups, aldehydes groups, ketone
groups, carboxylic acid groups, acyl groups (for example carboxylic
acid derivatives such as esters and amides), amine groups, nitro
groups, and the like. For example, the 4-methylphenyl radical is a
C.sub.7 aromatic radical comprising a methyl group, the methyl
group being a functional group which is an alkyl group. Similarly,
the 2-nitrophenyl group is a C.sub.6 aromatic radical comprising a
nitro group, the nitro group being a functional group. Aromatic
radicals include halogenated aromatic radicals such as
4-trifluoromethylphenyl,
hexafluoroisopropylidenebis(4-phen-1-yloxy) (i.e.,
--OPhC(CF.sub.3).sub.2PhO--), 4-chloromethylphen-1-yl,
3-trifluorovinyl-2-thienyl, 3-trichloromethylphen-1-yl (i.e.,
3-CCl.sub.3Ph-), 4-(3-bromoprop-1-yl)phen-1-yl (i.e.,
4-BrCH.sub.2CH.sub.2CH.sub.2Ph-), and the like. Further examples of
aromatic radicals include 4-allyloxyphen-1-oxy, 4-aminophen-1-yl
(i.e., 4-H.sub.2NPh-), 3-aminocarbonylphen-1-yl (i.e.,
NH.sub.2COPh-), 4-benzoylphen-1-yl,
dicyanomethylidenebis(4-phen-1-yloxy) (i.e.,
--OPhC(CN).sub.2PhO--), 3-methylphen-1-yl,
methylenebis(4-phen-1-yloxy) (i.e., --OPhCH.sub.2PhO--),
2-ethylphen-1-yl, phenylethenyl, 3-formyl-2-thienyl,
2-hexyl-5-furanyl, hexamethylene-1,6-bis(4-phen-1-yloxy) (i.e.,
--OPh(CH.sub.2).sub.6PhO--), 4-hydroxymethylphen-1-yl (i.e.,
4-HOCH.sub.2Ph-), 4-mercaptomethylphen-1-yl (i.e.,
4-HSCH.sub.2Ph-), 4-methylthiophen-1-yl (i.e., 4-CH.sub.3SPh-),
3-methoxyphen-1-yl, 2-methoxycarbonylphen-1-yloxy (e.g., methyl
salicyl), 2-nitromethylphen-1-yl (i.e., 2-NO.sub.2CH.sub.2Ph),
3-trimethylsilylphen-1-yl, 4-t-butyldimethylsilylphenl-1-yl,
4-vinylphen-1-yl, vinylidenebis(phenyl), and the like. The term "a
C.sub.3-C.sub.10 aromatic radical" includes aromatic radicals
containing at least three but no more than 10 carbon atoms. The
aromatic radical 1-imidazolyl (C.sub.3H.sub.2N.sub.2--) represents
a C.sub.3 aromatic radical. The benzyl radical (C.sub.7H.sub.7--)
represents a C.sub.7 aromatic radical.
[0028] As used herein the term "cycloaliphatic radical" refers to a
radical having a valence of at least one, and comprising an array
of atoms which is cyclic but which is not aromatic. As defined
herein a "cycloaliphatic radical" does not contain an aromatic
group. A "cycloaliphatic radical" may comprise one or more
noncyclic components. For example, a cyclohexylmethyl group
(C.sub.6H.sub.11CH.sub.2--) is an cycloaliphatic radical which
comprises a cyclohexyl ring (the array of atoms which is cyclic but
which is not aromatic) and a methylene group (the noncyclic
component). The cycloaliphatic radical may include heteroatoms such
as nitrogen, sulfur, selenium, silicon and oxygen, or may be
composed exclusively of carbon and hydrogen. For convenience, the
term "cycloaliphatic radical" is defined herein to encompass a wide
range of functional groups such as alkyl groups, alkenyl groups,
alkynyl groups, haloalkyl groups, conjugated dienyl groups, alcohol
groups, ether groups, aldehyde groups, ketone groups, carboxylic
acid groups, acyl groups (for example carboxylic acid derivatives
such as esters and amides), amine groups, nitro groups, and the
like. For example, the 4-methylcyclopent-1-yl radical is a C.sub.6
cycloaliphatic radical comprising a methyl group, the methyl group
being a functional group which is an alkyl group. Similarly, the
2-nitrocyclobut-1-yl radical is a C.sub.4 cycloaliphatic radical
comprising a nitro group, the nitro group being a functional group.
A cycloaliphatic radical may comprise one or more halogen atoms
which may be the same or different. Halogen atoms include, for
example; fluorine, chlorine, bromine, and iodine. Cycloaliphatic
radicals comprising one or more halogen atoms include
2-trifluoromethylcyclohex-1-yl, 4-bromodifluoromethylcyclooct-1-yl,
2-chlorodifluoromethylcyclohex-1-yl,
hexafluoroisopropylidene-2,2-bis(cyclohex4-yl) (i.e.,
--C.sub.6H.sub.10C(CF.sub.3).sub.2C.sub.6H.sub.10--),
2-chloromethylcyclohex-1-yl, 3-difluoromethylenecyclohex-1-yl,
4-trichloromethylcyclohex-1-yloxy,
4-bromodichloromethylcyclohex-1-ylthio, 2-bromoethylcyclopent-1-yl,
2-bromopropylcyclohex-1-yloxy (e.g.,
CH.sub.3CHBrCH.sub.2C.sub.6H.sub.10O--), and the like. Further
examples of cycloaliphatic radicals include
4-allyloxycyclohex-1-yl, 4-aminocyclohex-1-yl (i.e.,
H.sub.2NC.sub.6H.sub.10--), 4-aminocarbonylcyclopent-1-yl (i.e.,
NH.sub.2COC.sub.5H.sub.8--), 4-acetyloxycyclohex-1-yl,
2,2-dicyanoisopropylidenebis(cyclohex-4-yloxy) (i.e.,
--OC.sub.6H.sub.10C(CN).sub.2C.sub.6H.sub.10O--),
3-methylcyclohex-1-yl, methylenebis(cyclohex-4-yloxy) (i.e.,
--OC.sub.6H.sub.10CH.sub.2C.sub.6H.sub.10O--),
1-ethylcyclobut-1-yl, cyclopropylethenyl,
3-formyl-2-terahydrofuranyl, 2-hexyl-5-tetrahydrofuranyl,
hexamethylene-1,6-bis(cyclohex-4-yloxy) (i.e.,
--OC.sub.6H.sub.10(CH.sub.2).sub.6C.sub.6H.sub.10O--),
4-hydroxymethylcyclohex-1-yl (i.e., 4-HOCH.sub.2C.sub.6H.sub.10--),
4-mercaptomethylcyclohex-1-yl (i.e.,
4-HSCH.sub.2C.sub.6H.sub.10--), 4-methylthiocyclohex-1-yl (i.e.,
4-CH.sub.3SC.sub.6H.sub.10--), 4-methoxycyclohex-1-yl,
2-methoxycarbonylcyclohex-1-yloxy
(2-CH.sub.3OCOC.sub.6H.sub.10O--), 4-nitromethylcyclohex-1-yl
(i.e., NO.sub.2CH.sub.2C.sub.6H.sub.10--),
3-trimethylsilylcyclohex-1-yl,
2-t-butyldimethylsilylcyclopent-1-yl,
4-trimethoxysilylethylcyclohex-1-yl (e.g.,
(CH.sub.3O).sub.3SiCH.sub.2CH.sub.2C.sub.6H.sub.10--),
4-vinylcyclohexen-1-yl, vinylidenebis(cyclohexyl), and the like.
The term "a C.sub.3-C.sub.10 cycloaliphatic radical" includes
cycloaliphatic radicals containing at least three but no more than
10 carbon atoms. The cycloaliphatic radical 2-tetrahydrofuranyl
(C.sub.4H.sub.7O--) represents a C.sub.4 cycloaliphatic radical.
The cyclohexylmethyl radical (C.sub.6H.sub.11CH.sub.2--) represents
a C.sub.7 cycloaliphatic radical.
[0029] The present invention provides methods for optical data
storage use in holographic data storage and retrieval. These
holographic storage media include an optically transparent
substrate comprising an optically transparent plastic material and
at least one photochemically active dye. The photochemically active
dye has desirable optical properties, such as a relatively low
absorption cross-section while having a relatively high refractive
index change and/or relatively high quantum efficiency. High
quantum efficiency also leads to a higher sensitivity since
sensitivity is directly proportional to the product of quantum
efficiency and refractive index change (defined as .DELTA.n).
Writing of data as a hologram into the optically transparent
substrate comprising the photochemical dye is due to the dye
undergoing a photochemical conversion at the write wavelength,
thereby producing a modified optically transparent substrate
comprising at least one optically readable datum. The sensitivity
of a dye-doped data storage material is dependent upon the
concentration of the dye (N.sub.0), the dye's absorption
cross-section at the recording wavelength, the quantum efficiency
QE of the photochemical transition, and the index change of the dye
molecule for a unit dye density (.DELTA.n.sub.0/N.sub.0). However,
as the product of dye concentration and the absorption
cross-section increases, the disc becomes opaque, which complicates
both recording and readout. Therefore, dyes of interest for
achieving high M/#s are those materials that undergo a partial
photochemical transformation accompanied with a high refractive
index change and a high quantum efficiency at the wavelength that
is used for writing data, one that is removed from the main
UV-visible absorption peak of the dye.
[0030] A photochemically active dye may be described as a dye
molecule that has an optical absorption resonance characterized by
a center wavelength associated with the maximum absorption and a
spectral width (full width at half of the maximum, FWHM) of less
than 500 nanometers (hereinafter abbreviated as "nm"). In addition,
the photochemically active dye molecule undergoes a partial light
induced chemical reaction when exposed to light with a wavelength
within the absorption range to form at least one photo-product.
This reaction can be a photo-decomposition reaction, such as
oxidation, reduction, or bond breaking to form smaller
constituents, or a molecular rearrangement, such as a sigmatropic
rearrangement, or addition reactions including pericyclic
cycloadditions. Thus in an embodiment, data storage in the form of
holograms is achieved wherein the photo-product is patterned (for
example, in a graded fashion) within the modified optically
transparent substrate to provide the at least one optically
readable datum.
[0031] The photochemically active dye (hereinafter sometimes
referred to as "dye") is selected and utilized on the basis of
several characteristics, including the ability to change the
refractive index of the dye upon exposure to light; the efficiency
with which the light creates the refractive index change; and the
separation between the wavelength at which the dye shows an maximum
absorption and the desired wavelength or wavelengths to be used for
storing and/or reading the data. The choice of the photochemically
active dye depends upon many factors, such as sensitivity (S) of
the holographic storage media, concentration (N.sub.0) of the
photochemically active dye, the dye's absorption cross section
(.sigma.) at the recording wavelength, the quantum efficiency (QE)
of the photochemical conversion of the dye, and the refractive
index change per unit dye density (i.e., .DELTA.n/N.sub.0). Of
these factors, QE, .DELTA.n/N.sub.0, and .sigma. are more important
factors which affect the sensitivity (S) and also information
storage capacity (M/#). Preferred photochemically active dyes are
those that show a high refractive index change per unit dye density
(.DELTA.n/N.sub.0) (as explained previously), a high quantum
efficiency in the photochemical conversion step, and a low
absorption cross-section at the wavelength of the electromagnetic
radiation used for the photochemical conversion.
[0032] The photochemically active dye is one that is capable of
being written and read by electromagnetic radiation. It is
desirable to use dyes that can be written (with a signal beam) and
read (with a read beam) using actinic radiation i.e., radiation
having a wavelength from about 300 nm to about 1,100 nm. The
wavelengths at which writing and reading are accomplished are about
300 nm to about 800 nm. In one embodiment, the writing and reading
are accomplished at a wavelength of about 400 nm to about 600 nm.
In another embodiment, the writing and reading are accomplished at
a wavelength of about 400 to about 550 nanometers. In still another
embodiment, the reading wavelength is such that it is shifted by 0
nm to about 400 nm from the writing wavelength. Exemplary
wavelengths at which writing and reading are accomplished are about
405 nanometers and about 532 nanometers. In an embodiment, the
photochemically active dye is a vicinal diarylethene. In another
embodiment, the photochemically active dye is a photo-product
derived from a vicinal diarylethene. In still another embodiment,
the photochemically active dye is a nitrone. In still yet another
embodiment, the photochemically active dye is a nitrostilbene. Any
combination comprising two or more members selected from the group
consisting of a vicinal diarylethene, a nitrone, a photo-product
derived from a vicinal diarylethene, and a nitrostilbene can also
be used.
[0033] An exemplary class of vicinal diarylethene compounds can be
represented by generic structure (I), ##STR1##
[0034] wherein "e" is 0 or 1; R.sup.1 is a bond, an oxygen atom, a
substituted nitrogen atom, a sulfur atom, a selenium atom, a
divalent C.sub.1-C.sub.20 aliphatic radical, a halogenated divalent
C.sub.1-C.sub.20 aliphatic radical, a divalent C.sub.3-C.sub.20
cycloaliphatic radical, a halogenated divalent C.sub.1-C.sub.20
cycloaliphatic radical, or a divalent C.sub.2-C.sub.30 aromatic
radical; Ar.sup.1 and Ar.sup.2 are each independently a
C.sub.2-C.sub.40 aromatic radical, or a C.sub.2-C.sub.40
heteroaromatic radical; and Z.sup.1 and Z.sup.2 are independently a
bond, a hydrogen atom, a monovalent C.sub.1-C.sub.20 aliphatic
radical, divalent C.sub.1-C.sub.20 aliphatic radical, a monovalent
C.sub.3-C.sub.20 cycloaliphatic radical, a divalent
C.sub.3-C.sub.20 cycloaliphatic radical, a monovalent
C.sub.2-C.sub.30 aromatic radical, or a divalent C.sub.2-C.sub.30
aromatic radical. The Table below illustrates individual vicinal
diarylethene compounds encompassed by the chemical genus
represented by formula I. It should be noted that in the exemplary
structures listed in the table each of the aromatic radicals
Ar.sup.1 and Ar.sup.2 are identical as are the groups Z.sup.1 and
Z.sup.2. It will be understood by those skilled in the art that
Ar.sup.1 may differ in structure from Ar.sup.2 and that Z.sup.1 may
differ in structure from Z.sup.2, and that such species are
encompassed within generic structure I and are included within the
scope of the instant invention. TABLE-US-00001 Example R.sup.1 "e"
Ar.sup.1 & Ar.sup.2 Z.sup.1 & Z.sup.2 I-1 ##STR2## 1
##STR3## bond I-2 ##STR4## 1 ##STR5## bond I-3 ##STR6## 1 ##STR7##
bond I-4 ##STR8## 1 ##STR9## bond I-5 -- 0 ##STR10## CF.sub.3 I-6
##STR11## 1 ##STR12## bond I-7 ##STR13## 1 ##STR14## bond
[0035] In another embodiment, e is 0, and Z.sup.1 and Z.sup.2
C.sub.1-C.sub.5 alkyl, C.sub.1-C.sub.5 perfluoroalkyl, or CN. In
still another embodiment, e is 1, and Z.sup.1 and Z.sup.2 are
independently CH.sub.2, CF.sub.2, or C.dbd.O. In yet another
embodiment, Ar.sup.1 and Ar.sup.2 are each independently an
aromatic radical selected from the group consisting of phenyl,
anthracenyl, phenanthrenyl, pyridinyl, pyridazinyl, 1H-phenalenyl
and naphthyl, optionally substituted by one or more substituents,
wherein the substituents are each independently C.sub.1-C.sub.3
alkyl, C.sub.1-C.sub.3 perfluoroalkyl, C.sub.1-C.sub.3 alkoxy, or
fluorine. In yet another embodiment at least one of Ar.sup.1 and
Ar.sup.2 comprises one or more aromatic moieties selected from the
group consisting of structures (II), (III), and (IV), ##STR15##
wherein R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are hydrogen, a
halogen atom, a nitro group, a cyano group, a C.sub.1-C.sub.10
aliphatic radical, a C.sub.3-C.sub.10 cycloaliphatic radical, or a
C.sub.2-C.sub.10 aromatic radical; R.sup.7 is independently at each
occurrence a halogen atom, a nitro group, a cyano group, a
C.sub.1-C.sub.10 aliphatic radical, a C.sub.3-C.sub.10
cycloaliphatic radical, or a C.sub.2-C.sub.10 aromatic radical; "b"
is an integer from and including 0 to and including 4; X and Y are
selected from the group consisting of sulfur, selenium, oxygen, NH,
and nitrogen substituted by a C.sub.1-C.sub.10 aliphatic radical, a
C.sub.3-C.sub.10 cycloaliphatic radical, or a C.sub.2-C.sub.10
aromatic radical; and Q is CH or N. In one embodiment, at least one
of R.sup.3, R.sup.4, R.sup.5, and R.sup.6 is selected from the
group consisting of hydrogen, fluorine, chlorine, bromine,
C.sub.1-C.sub.3 alkyl, C.sub.1-C.sub.3 perfluoroalkyl, cyano,
phenyl, pyridyl, isoxazolyl, --CHC(CN).sub.2.
[0036] As mentioned previously, preferred photochemically active
dyes are those that show a high refractive index change, a high
quantum efficiency in the photochemical conversion step, and a low
absorption cross-section at the wavelength of the electromagnetic
radiation used for the photochemical conversion. One such example
of a suitable photochemically active dye is illustrated by the
vicinal diarylethene (V), ##STR16## which can be named as
1,2-bis{2-(4-methoxyphenyl)-5-methylthien-4-yl}-3,3,4,4,5,5-hexafluorocyc-
lopent-1-ene. Compound (V) shows a UV absorbance of about 1 at
about 600 nanometers, the wavelength at which it cyclizes
intramolecularly, and a high QE of about 0.8 for the cyclization
step. Vicinal diarylethene (V) is also represented in the Table
above as Example I-1 wherein, with reference to generic structure
I, R.sup.1 is a perfluorotrimethylene group, "e" is 1, Z.sup.1 and
Z.sup.2 are each bonds, and Ar.sup.1 and Ar.sup.2 are each
2-(4-methoxyphenyl)-5-methylthien-4-yl moieties.
[0037] Other examples of suitable vicinal diarylethenes that can be
used as photochemically active dyes include
diarylperfluorocyclopentenes, diarylmaleic anhydrides,
diarylmaleimides, or a combination comprising at least one of the
foregoing diarylethenes. The vicinal diarylethenes can be prepared
using methods known in the art.
[0038] The vicinal diarylethenes can be reacted in the presence of
actinic radiation (i.e. radiation that can produce a photochemical
reaction), such as light. In one embodiment, an exemplary vicinal
diarylethene can undergo a reversible cyclization reaction in the
presence of light (hv) according to the following equation (7),
##STR17## where X, Z R.sup.1 and e have the meanings indicated
above. The cyclization reactions can be used to produce holograms.
The holograms can be produced by using radiation to effect the
cyclization reaction or the reverse ring-opening reaction. Thus, in
an embodiment, a photo-product derived from a vicinal diarylethene
can be used as a photochemically active dye. Such photo-products
derived from the vicinal diarylethene can be represented by a
formula (VI), ##STR18## wherein "e", R.sup.1, Z.sup.1, and Z.sup.2
are as described for the vicinal diarylethene having formula (I), A
and B are fused rings, and R.sup.8 and R.sup.9 are each
independently a hydrogen atom, an aliphatic radical, a
cycloaliphatic radical, or an aromatic radical. One or both fused
rings A and B may comprise carbocyclic rings which do not have
heteroatoms. In another embodiment, the fused rings A and B may
comprise one or more heteroatoms selected from the group consisting
of oxygen, nitrogen, and sulfur. Non-limiting examples of compounds
falling within the scope of formula (VI) include the compounds
(VII) and (VIII) ##STR19## wherein R.sup.10 is independently at
each occurrence a hydrogen atom, a methoxy radical, or a
trifluoromethyl radical.
[0039] Nitrones can also be used as photochemically active dyes for
producing the holographic data storage media. An exemplary nitrone
generally comprises an aryl nitrone structure represented by the
structure (IX), ##STR20## wherein Ar.sup.3 is an aromatic radical,
each of R.sup.11, R.sup.12, and R.sup.13 is a hydrogen atom, an
aliphatic radical, a cycloaliphatic radical, or an aromatic
radical; R.sup.14 is an aliphatic radical (for example, an
isopropyl) or an aromatic radical, and "n" is an integer having a
value of from 0 to 4. In an embodiment, the radical R.sup.14
comprises one or more electron withdrawing substituents selected
from the group consisting of ##STR21## wherein R.sup.15-R.sup.17
are independently a C.sub.1-C.sub.10 aliphatic radical, a
C.sub.3-C.sub.10 cycloaliphatic radical, or a C.sub.2-C.sub.10
aromatic radical.
[0040] As can be seen from structure (IX), the nitrones may be
.alpha.-aryl-N-arylnitrones or conjugated analogs thereof in which
the conjugation is between the aryl group and an .alpha.-carbon
atom. The .alpha.-aryl group is frequently substituted, often by a
dialkylamino group, in which the alkyl groups contain 1 to about 4
carbon atoms. Suitable, non-limiting examples of nitrones include
.alpha.-(4-diethylaminophenyl)-N-phenylnitrone;
.alpha.-(4-diethylaminophenyl)-N-(4-chlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(3,4-dichlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-carbethoxyphenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-acetylphenyl)-nitrone,
.alpha.-(4-dimethylaminophenyl)-N-(4-cyanophenyl)-nitrone,
.alpha.-(4-methoxyphenyl)-N-(4-cyanophenyl)nitrone,
.alpha.-(9-julolidinyl)-N-phenylnitrone,
.alpha.-(9-julolidinyl)-N-(4-chlorophenyl)nitrone,
.alpha.-(4-Dimethylamino)styryl-N-phenyl Nitrone,
.alpha.-Styryl-N-phenyl nitrone,
.alpha.-[2-(1,1-diphenylethenyl)]-N-phenylnitrone,
.alpha.-[2-(1-phenylpropenyl)]-N-phenylnitrone, or a combination
comprising at least one of the foregoing nitrones.
[0041] In another embodiment, the photochemically active dye is a
nitrostilbene compound. Nitrostilbene compounds are illustrated by
4-dimethylamino-2',4'-dinitrostilbene,
4-dimethylamino4'-cyano-2'-nitrostilbene,
4-hydroxy-2',4'-dinitrostilbene, and the like. The nitrostilbene
can be a cis isomer, a trans isomer, or mixtures of the cis and
trans isomers. Thus, in another embodiment, the photochemically
active dye useful for producing a holographic data storage medium
comprises at least one member selected from the group consisting of
4-dimethylamino-2',4'-dinitrostilbene,
4-dimethylamino-4'-cyano-2'-nitrostilbene,
4-hydroxy-2',4'-dinitrostilbene, 4-methoxy-2',4'-dinitrostilbene,
.alpha.-(4-diethylaminophenyl)-N-phenylnitrone;
.alpha.-(4-diethylaminophenyl)-N-(4-chlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(3,4-dichlorophenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-carbethoxyphenyl)-nitrone,
.alpha.-(4-diethylaminophenyl)-N-(4-acetylphenyl)-nitrone,
.alpha.-(4-dimethylaminophenyl)-N-(4-cyanophenyl)-nitrone,
.alpha.-(4-methoxyphenyl)-N-(4-cyanophenyl)nitrone,
.alpha.-(9-julolidinyl)-N-phenylnitrone,
.alpha.-(9-julolidinyl)-N-(4-chlorophenyl)nitrone,
.alpha.-[2-(1,1-diphenylethenyl)]-N-phenylnitrone, and
.alpha.-[2-(1-phenylpropenyl)]-N-phenylnitrone.
[0042] Upon exposure to electromagnetic radiation, nitrones undergo
unimolecular cyclization to an oxaziridine illustrated by structure
(X), ##STR22## wherein Ar.sup.3, R.sup.11-R.sup.14, and n have the
same meaning as denoted above for the structure (IX).
[0043] The photochemically active dye is used in an amount from
about 0.1 to about 10 weight percent in an embodiment, from about 1
weight percent to about 4 weight percent in another embodiment, and
from about 4 weight percent to about 7 weight percent in still
another embodiment, based on a total weight of the optically
transparent substrate.
[0044] The optically transparent plastic materials used in
producing the holographic data storage media can comprise any
plastic material having sufficient optical quality, e.g., low
scatter, low birefringence, and negligible losses at the
wavelengths of interest, to render the data in the holographic
storage material readable. Organic polymeric materials, such as for
example, oligomers, polymers, dendrimers, ionomers, copolymers such
as for example, block copolymers, random copolymers, graft
copolymers, star block copolymers; or the like, or a combination
comprising at least one of the foregoing polymers can be used.
Thermoplastic polymers or thermosetting polymers can be used.
Examples of suitable thermoplastic polymers include polyacrylates,
polymethacrylates, polyamides, polyesters, polyolefins,
polycarbonates, polystyrenes, polyesters, polyamideimides,
polyarylates, polyarylsulfones, polyethersulfones, polyphenylene
sulfides, polysulfones, polyimides, polyetherimides,
polyetherketones, polyether etherketones, polyether ketone ketones,
polysiloxanes, polyurethanes, polyarylene ethers, polyethers,
polyether amides, polyether esters, or the like, or a combination
comprising at least one of the foregoing thermoplastic polymers.
Some more possible examples of suitable thermoplastic polymers
include, but are not limited to, amorphous and semi-crystalline
thermoplastic polymers and polymer blends, such as: polyvinyl
chloride, linear and cyclic polyolefins, chlorinated polyethylene,
polypropylene, and the like; hydrogenated polysulfones, ABS resins,
hydrogenated polystyrenes, syndiotactic and atactic polystyrenes,
polycyclohexyl ethylene, styrene-acrylonitrile copolymer,
styrene-maleic anhydride copolymer, and the like; polybutadiene,
polymethylmethacrylate (PMMA), methyl methacrylate-polyimide
copolymers; polyacrylonitrile, polyacetals, polyphenylene ethers,
including, but not limited to, those derived from
2,6-dimethylphenol and copolymers with 2,3,6-trimethylphenol, and
the like; ethylene-vinyl acetate copolymers, polyvinyl acetate,
ethylene-tetrafluoroethylene copolymer, aromatic polyesters,
polyvinyl fluoride, polyvinylidene fluoride, and polyvinylidene
chloride.
[0045] In some embodiments, the thermoplastic polymer used in the
methods disclosed herein as a substrate is made of a polycarbonate.
The polycarbonate may be an aromatic polycarbonate, an aliphatic
polycarbonate, or a polycarbonate comprising both aromatic and
aliphatic structural units.
[0046] As used herein, the term "polycarbonate" includes
compositions having structural units of the structure (XI),
##STR23## where R.sup.15 is an aliphatic, aromatic or a
cycloaliphatic radical. In an embodiment, the polycarbonate
comprises structural units of the structure (XII):
-A.sup.1-Y.sup.1-A.sup.2- (XII) wherein each of A.sup.1 and A.sup.2
is a monocyclic divalent aryl radical and Y.sup.1 is a bridging
radical having zero, one, or two atoms which separate A.sup.1 from
A.sup.2. In an exemplary embodiment, one atom separates A.sup.1
from A.sup.2. Illustrative, non-limiting examples of radicals of
this type are --O--, --S--, --S(O)--, --S(O).sub.2--, --C(O)--,
methylene, cyclohexyl-methylene, 2-ethylidene, isopropylidene,
neopentylidene, cyclohexylidene, cyclopentadecylidene,
cyclododecylidene, adamantylidene, and the like. Some examples of
such bisphenol compounds are bis(hydroxyaryl)ethers such as
4,4'-dihydroxy diphenylether, 4,4'-dihydroxy-3,3'-dimethylphenyl
ether, or the like; bis(hydroxy diaryl)sulfides, such as
4,4'-dihydroxy diphenyl sulfide, 4,4'-dihydroxy-3,3'-dimethyl
diphenyl sulfide, or the like; bis(hydroxy diaryl) sulfoxides, such
as, 4,4'-dihydroxy diphenyl sulfoxides,
4,4'-dihydroxy-3,3'-dimethyl diphenyl sulfoxides, or the like;
bis(hydroxy diaryl)sulfones, such as 4,4'-dihydroxy diphenyl
sulfone, 4,4'-dihydroxy-3,3'-dimethyl diphenyl sulfone, or the
like; or combinations comprising at least one of the foregoing
bisphenol compounds. In another embodiment, zero atoms separate
A.sup.1 from A.sup.2, with an illustrative example being biphenol.
The bridging radical Y.sup.1 can be a hydrocarbon group, such as,
for example, methylene, cyclohexylidene or isopropylidene, or aryl
bridging groups.
[0047] Any of the dihydroxy aromatic compounds known in the art can
be used to make the polycarbonates. Examples of dihydroxy aromatic
compounds include, for example, compounds having general structure
(XIII), ##STR24## wherein R.sup.16 and R.sup.17 each independently
represent a halogen atom, or a aliphatic, aromatic, or a
cycloaliphatic radical; a and b are each independently integers
from 0 a to 4; and X.sup.c represents one of the groups of
structure (XIV), ##STR25## wherein R.sup.18 and R.sup.19 each
independently represent a hydrogen atom or a aliphatic, aromatic or
a cycloaliphatic radical; and R.sup.20 is a divalent hydrocarbon
group. Some illustrative, non-limiting examples of suitable
dihydroxy aromatic compounds include dihydric phenols and the
dihydroxy-substituted aromatic hydrocarbons such as those disclosed
by name or structure (generic or specific) in U.S. Pat. No.
4,217,438. Polycarbonates comprising structural units derived from
bisphenol A are preferred since they are relatively inexpensive and
commercially readily available. A nonexclusive list of specific
examples of the types of bisphenol compounds that may be
represented by structure (XIII) includes the following:
1,1-bis(4-hydroxyphenyl) methane; 1,1-bis(4-hydroxyphenyl) ethane;
2,2-bis(4-hydroxyphenyl) propane (hereinafter "bisphenol A" or
"BPA"); 2,2-bis(4-hydroxyphenyl) butane; 2,2-bis(4-hydroxyphenyl)
octane; 1,1-bis(4-hydroxyphenyl) propane; 1,1-bis(4-hydroxyphenyl)
n-butane; bis(4-hydroxyphenyl) phenylmethane;
2,2-bis(4-hydroxy-3-methylphenyl) propane (hereinafter "DMBPA");
1,1-bis(4-hydroxy-t-butylphenyl) propane; bis(hydroxyaryl) alkanes
such as 2,2-bis(4-hydroxy-3-bromophenyl) propane;
1,1-bis(4-hydroxyphenyl) cyclopentane; 9,9'-bis(4-hydroxyphenyl)
fluorene; 9,9'-bis(4-hydroxy-3-methylphenyl) fluorene;
4,4'-biphenol; and bis(hydroxyaryl) cycloalkanes such as
1,1-bis(4-hydroxyphenyl) cyclohexane and
1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (hereinafter "DMBPC");
and the like, as well as combinations comprising at least one of
the foregoing bisphenol compound.
[0048] Polycarbonates can be produced by any of the methods known
in the art. Branched polycarbonates are also useful, as well as
blends of linear polycarbonates and branched polycarbonates.
Preferred polycarbonates are based on bisphenol A. Preferably, the
weight average molecular weight of the polycarbonate is about 5,000
to about 100,000 atomic mass units, more preferably about 10,000 to
about 65,000 atomic mass units, and most preferably about 15,000 to
about 35,000 atomic mass units. Other specific examples of a
suitable thermoplastic polymer for use in forming the holographic
data storage media include Lexan.RTM., a polycarbonate; and
Ultem.RTM., an amorphous polyetherimide, both of which are
commercially available from General Electric Company.
[0049] Examples of useful thermosetting polymers include those
selected from the group consisting of an epoxy, a phenolic, a
polysiloxane, a polyester, a polyurethane, a polyamide, a
polyacrylate, a polymethacrylate, or a combination comprising at
least one of the foregoing thermosetting polymers.
[0050] The photochemically active dye may be admixed with other
additives to form a photo-active material. Examples of such
additives include heat stabilizers; antioxidants; light
stabilizers; plasticizers; antistatic agents; mold releasing
agents; additional resins; binders, blowing agents; and the like,
as well as combinations of the foregoing additives. The
photo-active materials are used for manufacturing holographic data
storage media.
[0051] Cycloaliphatic and aromatic polyesters can be used as
binders for preparing the photo-active material. These are suitable
for use with thermoplastic polymers, such as polycarbonates, to
form the optically transparent substrate. These polyesters are
optically transparent, and have improved weatherability, low water
absorption and good melt compatibility with the polycarbonate
matrix. Cycloaliphatic polyesters are generally prepared by
reaction of a diol with a dibasic acid or an acid derivative, often
in the presence of a suitable catalyst.
[0052] Generally, the polymers used for forming the optically
transparent substrate, and the holographic data storage medium
should be capable of withstanding the processing parameters, such
as for example during the step of including the dye and application
of any coating or subsequent layers and molding into final format;
and subsequent storage conditions. Suitable thermoplastic polymers
have glass transition temperatures of about 100.degree. C. or
greater in an embodiment, about 150.degree. C. or greater in
another embodiment, and about 200.degree. C. or greater in still
another embodiment. Exemplary thermoplastic polymers having glass
transition temperatures of 200.degree. C. or greater include
certain types of polyetherimides, polyimides, and combinations
comprising at least one of the foregoing.
[0053] As noted above, the effective photochemically active dye is
present in an amount from about 0.1 to about 10 weight percent,
based on the total weight of the optically transparent substrate,
and has a UV-visible absorbance in a range between about 0.1 and
about 1 at a wavelength in a range between about 300 nm and about
800 nm. Such photochemically active dyes are used in combination
with other materials, such as, for example, binders to form
photo-active materials, which in turn are used for manufacturing
holographic data storage media. In an embodiment, a film of an
optically transparent substrate comprising at least one optically
transparent plastic material and at least one photochemically
active dye is formed. Generally, the film is prepared by molding
techniques by using a molding composition that is obtained by
mixing the dye with an optically transparent plastic material.
Mixing can be conducted in machines such as a single or multiple
screw extruder, a Buss kneader, a Henschel, a helicone, an Eirich
mixer, a Ross mixer, a Banbury, a roll mill, molding machines such
as injection molding machines, vacuum forming machines, blow
molding machine, or then like, or a combination comprising at least
one of the foregoing machines. Alternatively, the dye and the
optically transparent plastic material may be dissolved in a
solution and films of the optically transparent substrate can be
spin cast from the solution.
[0054] After the mixing step, the data storage composition is
injection molded into an article that can be used for producing
holographic data storage media. The injection-molded article can
have any geometry. Examples of suitable geometries include circular
discs, square shaped plates, polygonal shapes, or the like. The
thickness of the articles can vary, from being at least 100
micrometers in an embodiment, and at least 250 micrometers in
another embodiment. Thickness of at least 250 micrometers is useful
in producing holographic data storage disks which are comparable to
the thickness of current digital storage discs.
[0055] The molded data storage medium thus produced can be used for
producing data storage articles, which can be used for storing data
in the form of holograms. The data storage medium in the data
storage article is irradiated with electromagnetic energy having a
first wavelength to form a modified optically transparent substrate
comprising at least one optically readable datum and at least one
photo-product of the photochemically active dye. The resulting
holographic data storage medium has the photo-product patterned
within the optically transparent substrate to provide at least one
optically readable datum. In one embodiment, the irradiation
facilitates a partial chemical conversion (also sometimes referred
to as "reaction") of the photochemically active dye to a
photo-product, for example, the cyclization reaction of the vicinal
diarylethene to a cyclized product, or the ring opening reaction of
the cyclized product to the vicinal diarylethene product, or
conversion of an aryl nitrone to an aryl oxaziridine product; or a
decomposition product derived from the oxaziridine, thereby
creating a hologram of the at least one optically readable
datum.
[0056] Reading of the stored holographic data can be achieved by a
read beam, which comprises irradiating the data storage medium with
electromagnetic energy. The read beam reads the data contained by
diffracted light from the hologram. In an embodiment, the read
wavelength can be between 350 and 1,100 nanometers (nm). In one
embodiment, the wavelengths of the data beam used for writing the
data as holograms and the read beam used for reading the stored
data are the same. In another embodiment, the wavelengths of the
data beam and the read beam are different from each other, and can
independently have a wavelength between 350 and 1,100 nanometers.
In still another embodiment, the read beam has a wavelength that is
shifted by 0 nm to about 400 nm from the wavelength of the write
beam.
[0057] The methods disclosed herein can be used for producing
holographic data storage media that can be used for bit-wise type
data storage in an embodiment, and page-wise type storage of data
in another embodiment. In still another embodiment, the methods can
be used for storing data in multiple layers of the data storage
medium.
[0058] The holographic data storage articles described hereinabove
are useful for recording data in the form of holograms and reading
the holographic data. The holographic data storage medium in the in
the holographic data storage article is irradiated with
electromagnetic energy having a first wavelength (the signal beam
or the write beam) having data to be written. This leads to the
formation of a modified optically transparent substrate comprising
at least one photo-product of the at least one photochemically
active dye (described previously), and at least one optically
readable datum. The data is then stored in the data storage medium
as a hologram. Then the holographic data storage medium is
irradiated with electromagnetic energy having a second wavelength
(the read beam) to read the hologram. In an embodiment, the read
beam has a wavelength that is shifted by 0 nanometer to about 400
nanometers from the signal beam's wavelength.
[0059] While the disclosure has been illustrated and described in
typical embodiments, it is not intended to be limited to the
details shown, since various modifications and substitutions can be
made without departing in any way from the spirit of the present
disclosure. As such, further modifications and equivalents of the
disclosure herein disclosed may occur to persons skilled in the art
using no more than routine experimentation, and all such
modifications and equivalents are believed to be within the spirit
and scope of the disclosure as defined by the following claims.
EXAMPLES
Example 1
Preparation of 4'-methoxy-2,4-dinitrostilbene
[0060] To a 2 liter 3-necked round-bottomed flask equipped with a
condenser, a Dean-Stark trap, a mechanical stirrer, nitrogen inlet,
heating mantle, thermometer, and a Therm-o-watch.RTM. temperature
controller, was added p-anisaldehyde (149.8 grams, 1.1 moles),
2,4-dinitrotoluene (182 grams, 1.0 mole), xylene (500 milliliters),
and piperidine (50 milliliters, 0.5 mole). The resulting mixture
was heated with the temperature on the Therm-o-watch.RTM.
temperature controller set at 145.degree. C. After stirring and
heating for about 2 hours, approximately 20 milliliters of water
had collected in the Dean-Stark trap. The reaction solution was
allowed to cool to room temperature, and then further cooled with
an ice water bath for an additional hour during which time the
desired product crystallized from the solution. The solid material
was filtered, rinsed with pentane, and dried in a vacuum oven at
100.degree. C. for 12 hours to give 257.1 grams (85.6 percent of
theory) of the desired product as a dark red crystalline solid.
Example 2
Preparation of .alpha.-(4-Dimethylamino)styryl-N-phenyl nitrone
[0061] To a 1-liter, 3-necked round-bottomed flask equipped with a
mechanical stirrer and a nitrogen inlet was added
phenylhydroxyamine (27.3 grams, 0.25 mole),
(4-dimethylamino)cinnamaldehyde (43.81 grams, 0.25 mole), and
ethanol (250 milliliters). To the resulting bright orange slurry
was added methanesulfonic acid (250 microliters) via a syringe. The
bright orange slurry turned to a deep red and all solids dissolved.
Within five minutes, an orange solid formed. Pentane (about 300
milliliters) was added to facilitate stirring of the reaction
mixture. The solid was filtered and dried in a vacuum oven at
80.degree. C. for several hours to give 55.9 grams (84 percent of
theory) of the desired product as a bright orange solid. The dye
has structure (XV): ##STR26##
Example 3
Preparation of .alpha.-Styryl-N-phenyl nitrone
[0062] N-Isopropylhydroxylamine hydrochloride (5.04 grams, 45.2
millimoles, 1 molar equivalent; available from Acros Organics) was
combined with trans-cinnamaldehyde (5.66 grams, 42.9 millimoles,
0.95 molar equivalent; available from Aldrich Chemical Company) in
16 milliliters of water. The rapidly stirred mixture started off as
an emulsion due to the low solubility of the trans-cinnamaldehyde.
After about one hour, the emulsion disappeared, and a homogeneous
light yellow solution resulted. After being stirred for four hours,
the reaction mixture was poured into methylene chloride and treated
with 26 milliliters of saturated aqueous sodium carbonate solution
(containing greater than 2 molar equivalents of sodium carbonate
base to insure consumption of hydrogen chloride by-product) such
that the pH was about 10.5. The phases were separated and the
aqueous phase was rinsed with additional methylene chloride. The
combined organic phase was separated, dried over anhydrous
magnesium sulfate, concentrated in vacuo, and dried under vacuum
overnight to produce 7.4 grams (91 percent of theory) of the
desired product that was determined to be pure by liquid
chromatography and further characterized by NMR spectroscopy.
UV-visible spectrum of the product in absolute ethanol revealed an
absorption maximum (.lamda..sub.max) at 330 nanometers. Exposure of
this dilute solution to a 390 nanometer light source converted the
nitrone to the corresponding oxaziradine with a shift of the
absorption maximum to 256 nanometers. All sample manipulations were
done in a dark room containing only red light to insure the
stability of .alpha.-styryl-N-phenyl nitrone. The dye has structure
(XVI): ##STR27##
Example 4
[0063] This Example describes the procedure for preparing a
.alpha.-(4-Dimethylamino)styryl-N-phenyl Nitrone--Polystyrene
blend, which was subsequently used for preparing molded disks
having a thickness of about 1.2 millimeters.
[0064] Ten kilograms of crystal polystyrene 1301 pellets (obtained
from Nova Chemicals) were ground to a coarse powder in a Retsch
mill and dried in a circulating air oven maintained at 80.degree.
C. for several hours. In a 10-liter Henschel mixer, 6.5 kilograms
of the dry polystyrene powder and 195 grams of
.alpha.-(4-dimethylamino)styryl-N-phenyl nitrone were blended to
form a homogeneous orange powder. The powder blend was then fed to
a WP 28 millimeter twin-screw extruder at 185.degree. C. to give
6.2 kilograms of dark orange pellets with a nominal dye content of
about 3 weight percent. This material was then further diluted with
additional crystal polystyrene 1301 pellets to make blends having
0.60 weight percent, 0.75 weight percent, 1 weight percent, and
1.24 weight percent of .alpha.-(4-dimethylamino)styryl-N-phenyl
nitrone. Each of these four diluted blend compositions was
re-processed with the WP 28 millimeter twin-screw extruder to form
homogeneously colored pellets.
[0065] Optical quality disks were prepared by injection molding the
four diluted blends (prepared as described above) with an ELECTRA
DISCO.TM. 50-ton all-electrical commercial CD/DVD (compact
disc/digital video disc) molding machine (available from Milacron
Inc.). Mirrored stampers were used for both surfaces. Cycle times
were generally set to about 10 seconds. Molding conditions were
varied depending upon the glass transition temperature and melt
viscosity of the polymer used, as well as the photochemically
active dye's thermal stability. Thus the maximum barrel temperature
was varied from about 200.degree. C. to about 375.degree. C.
Example 5
[0066] Procedures for preparing molded disks using the
Mini-jector.RTM.. The molding conditions varied depending upon the
nature of the polymer matrix used to incorporate the
photochemically active dye. Typical conditions used for molding OQ
(Optical Grade) polycarbonate and polystyrene based blends of the
photochemically active dyes are shown in Table 1. TABLE-US-00002
TABLE 1 OQ Polycarbonate Molding Parameters Powder Polystyrene
Powder Barrel Temp. (Rear) (.degree. F.) 500 400 Barrel Temp.
(Front) (.degree. F.) 540 395 Barrel Temp. (Nozzle) (.degree. F.)
540 395 Mold Temp. (.degree. F.) 200 100 Total Cycle Time (sec) 35
25 Switch Point (inch) 0.7 0.7 Injection Transition (inch) 0.22
0.22 Injection Boost Press. (psi) 950 850 Injection Hold Press.
(psi) 300 250
Example 6
[0067] Procedure for measuring UV-visible spectra of the
photochemically active dyes. All spectra were recorded on a
Cary/Varian 300 UV-visible spectrophotometer using injection-molded
disks having a thickness of about 1.2 millimeters. Spectra were
recorded in the range of 300 nanometers to 800 nanometers. Due to
disk-to-disk variations, no reference sample was used. Results of
the UV-visible absorption spectra measurements are shown in Table 2
as Examples 7-11.
[0068] The absorption reported in the table was calculated by
subtracting the average baseline in the range of 700-800 nanometers
for each sample tested from the measured absorption at either 405
nanometers or 532 nanometers. Since these compounds do not absorb
in the 700-800 nanometer range, this correction removed the
apparent absorption caused by reflections off the surfaces of the
disk and provided a more accurate representation of the absorbance
of the dye. The polymers used in these examples had little or no
absorption at 405 nanometers or 532 nanometers.
[0069] Examples 7-10 used .alpha.-(4-Dimethylamino)styryl-N-phenyl
nitrone as the photochemically active dye, and Example 11 used
.alpha.-styryl-N-phenyl nitrone. TABLE-US-00003 TABLE 2 Photo- Dye
con- Absorbance chemically centration Observation at Example Active
Dye (weight Wavelength observation Number Structure percent)
(nanometers) wavelength M# 7 XV 0.6 532 0.33 0.66 8 XV 0.75 532
0.42 0.86 9 XV 1 532 0.57 1.01 10 XV 1.24 532 0.7 1.28 11 XVI 2.9
405 0.58 2.5
[0070] The data in Table 2 shows that an M# of 0.5 or higher can be
achieved by using from about 0.1 to about 10 weight percent of a
dye, based on a total weight of the optically transparent
substrate, wherein the photochemically active dye has a UV-visible
absorbance in a range from about 0.1 to about 1 at a wavelength in
a range from about 300 nanometers to about 800 nanometers. The
results also show that high volumetric data storage capacities can
be achieved using photochemically active dyes that are efficient
and sensitive to electromagnetic energy, such as light without
interference from the main absorption peak of the dye.
* * * * *